ESP32 and Si7021 temperature sensor example

The  Si7021  I2C Humidity  and  Temperature  Sensor  is  a  monolithic  CMOS  IC integrating   humidity   and   temperature   sensor   elements,   an   analog-to-digital converter, signal processing, calibration data, and an I2C Interface. The Si7021 offers an accurate, low-power, factory-calibrated digital solution ideal for measuring humidity, dew-point, and temperature, in applications ranging from HVAC/R and asset tracking to industrial and consumer platforms.

Si7021

Features

Precision Relative Humidity Sensor ± 3% RH (max), 0–80% RH
High Accuracy Temperature Sensor ±0.4 °C (max), –10 to 85 °C
0 to 100% RH operating range
Up to –40 to +125 °C operating range
Wide operating voltage – (1.9 to 3.6 V)
Low Power Consumption – 150 μA active current

Parts Required

Here are the parts I used

Name	Link
ESP32		Aliexpress link Amazon Ebay
Si7021		Aliexpress link Ebay link Amazon Link
Connecting cables		Aliexpress link Amazon Ebay

Connection

esp32 and si7021

Code

No 3rd party libraries required

#include <Wire.h>

// SI7021 I2C address is 0x40(64)
#define si7021Addr 0x40

void setup()
{
  Wire.begin();
  Serial.begin(9600);
  Wire.beginTransmission(si7021Addr);
  Wire.endTransmission();
  delay(300);
}

void loop()
{
  unsigned int data[2];
  
  Wire.beginTransmission(si7021Addr);
  //Send humidity measurement command
  Wire.write(0xF5);
  Wire.endTransmission();
  delay(500);
    
  // Request 2 bytes of data
  Wire.requestFrom(si7021Addr, 2);
  // Read 2 bytes of data to get humidity
  if(Wire.available() == 2)
  {
    data[0] = Wire.read();
    data[1] = Wire.read();
  }
    
  // Convert the data
  float humidity  = ((data[0] * 256.0) + data[1]);
  humidity = ((125 * humidity) / 65536.0) - 6;

  Wire.beginTransmission(si7021Addr);
  // Send temperature measurement command
  Wire.write(0xF3);
  Wire.endTransmission();
  delay(500);
    
  // Request 2 bytes of data
  Wire.requestFrom(si7021Addr, 2);
  
  // Read 2 bytes of data for temperature
  if(Wire.available() == 2)
  {
    data[0] = Wire.read();
    data[1] = Wire.read();
  }

  // Convert the data
  float temp  = ((data[0] * 256.0) + data[1]);
  float celsTemp = ((175.72 * temp) / 65536.0) - 46.85;
  float fahrTemp = celsTemp * 1.8 + 32;
   
  // Output data to serial monitor
  Serial.print("Humidity : ");
  Serial.print(humidity);
  Serial.println(" % RH");
  Serial.print("Celsius : ");
  Serial.print(celsTemp);
  Serial.println(" C");
  Serial.print("Fahrenheit : ");
  Serial.print(fahrTemp);
  Serial.println(" F");
  delay(1000);
}

Testing

Open the serial monitor and you should see something like this

Humidity : 44.89 % RH
Celsius : 21.07 C
Fahrenheit : 69.93 F
Humidity : 45.25 % RH
Celsius : 22.14 C
Fahrenheit : 71.86 F
Humidity : 47.32 % RH
Celsius : 26.53 C
Fahrenheit : 79.76 F
Humidity : 49.03 % RH
Celsius : 28.33 C
Fahrenheit : 83.00 F
Humidity : 50.74 % RH
Celsius : 29.26 C
Fahrenheit : 84.66 F

Link